Years ago I had a winter beater that used ALOT of oil and it'd smoke alot if I feathered the gas and noticed that no one would then tailgate me.
I had another car which was pre-cat convertor and had true dual exhaust straight back so I made a "smoke machine" for those special occasions when you're already going faster than all other traffic, plenty of passing room, etc YET some jerk still wants to ride your tail.
I used a spare WW resevoir, filled with ATF, an old electric fuel pump and a momentary on switch. On demand, I'd hit the switch and it'd pump ATF into the intake manifold and the smoke was incredible, like an instant cloud blowing out two tailpipes. Trust me, the times I used it the tailgators dissappeared probably thinking that my engine blew.
I later tryed the device on a newer car but those with cat. convertors burn the oil too efficiently and one could damage the cat too so such a device only works well with older, pre-cat cars (pre-'75 in the US).
One can always slam on the brakes but with road-ragers or family members inside, that might not be a good idea.